This invention relates to a torque limiter incorporating a brake, and in particular to a device suitable for use in aerospace applications, for example at or adjacent the outboard ends of an aircraft wing.
It is known for a rotatable drive shaft to be provided which extends along the length of an aircraft wing and which is used to drive the actuators used to control the positions of, for example, wing mounted moveable flaps, slats or other flight control surfaces. The shaft is typically rotated, in use, by a motor located at an inboard position. A number of types of motor, for example of hydraulically powered or electrically powered form, are known for such use.
Torque limiting devices are often provided between the drive shaft and the actuators associated therewith, the torque limiting devices being arranged to apply a braking load to the drive shaft in the event that the torque being transmitted between the drive shaft and the actuator with which the torque limiter is associated exceeds a predetermined value typically due to a jam of the actuator or associated control surface. As a result, in the event of the applied torque becoming excessive, the drive shaft and all of the actuators associated therewith become locked against further movement. One form of torque limiting device used in such applications is a roller-jammer type device.
It is also known to provide a separate friction brake device typically towards the outboard end of the drive shaft, for example to allow the selective application of a braking load to the outboard end of the drive shaft in the event of a failure of the drive shaft or motor in order to brake the drive shaft and lock the control surfaces in position, preventing them from being moved by aerodynamic loads. GB2136526 describes a friction brake arrangement for use in such an application, the brake being electromagnetically operated in the event of a drive shaft failure being sensed.
The above arrangement of torque limiter and separate selective brake device results in an undesirable duplication of brake components within the two devices and increased weight and size of the control surface actuation system.
In aerospace applications it is desirable to be able to minimise the weight of components mounted upon the aircraft, as the carrying of unnecessary weight results in the aircraft operating relatively inefficiently.